### Problem
Users were confused because `<dyad-command>` tags were being hidden,
making it unclear what actions were available.

### Solution
Render dyad-command tags as visible buttons, so users can see and
interact with available commands (e.g., "restart").

Closes #1421
    
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## Summary by cubic
Show dyad-command tags as visible buttons in assistant responses so
users can see and trigger actions (e.g., restart). Closes #1421.

- **Bug Fixes**
  - Render dyad-command tags to buttons in DyadMarkdownParser.
  - Export mapActionToButton from ChatInput for reuse.
  - Support id/action/path attributes; safely no-op if parsing fails.

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